People from all walks of life have long considered the possibility of finding life on other planets. The fundamental issue in the question you pose is the definition of "life." Scientific advances in numerous fields have improved our ability to identify the factors that are required for an organism to...
People from all walks of life have long considered the possibility of finding life on other planets. The fundamental issue in the question you pose is the definition of "life." Scientific advances in numerous fields have improved our ability to identify the factors that are required for an organism to be considered alive. Physicist Stephen Hawking was especially lucid in laying out the different requirements. Here is part of his basic explanation:
One can define Life to be an ordered system that can sustain itself against the tendency to disorder, and can reproduce itself. That is, it can make similar, but independent, ordered systems. To do these things, the system must convert energy in some ordered form, like food, sunlight, or electric power, into disordered energy, in the form of heat.
The second crucial issue is the conditions on another planet that would support life, which are almost certainly different than those on Earth. Closely related to this is what kind of life forms would develop in different environments. Hawkins also summarized some of these requirements, or likely conditions:
What we normally think of as 'life' is based on chains of carbon atoms, with a few other atoms, such as nitrogen or phosphorous. One can speculate that one might have life with some other chemical basis, such as silicon, but carbon seems the most favorable case, because it has the richest chemistry. That carbon atoms should exist at all, with the properties that they have, requires a fine adjustment of physical constants, such as the QCD scale, the electric charge, and even the dimension of space-time.
The logical extension of such considerations, to determine if homo sapiens might ever contact other creatures that resemble our species, is far more complicated. If humans do land on another planet, they will certainly have some impact on that planet's environment and on any life forms present there.
One analogy with European contact in the Americas is the rapid spread of disease, which decimated the Indigenous people, who had little means of resistance. Therefore, despite any good intentions or lack of desire to colonize another planet or the life forms found there, it is only logical to assume that the mere presence of extraterrestrial visitors could easily damage, if not destroy, the life-forms indigenous to that place.